1. Field of the Invention
The present invention relates to improvements in a diaphragm clutch, more particularly to improvements in a support structure for fulcruming the diaphragm spring serving as a release member for the engagement and disengagement of the clutch.
2. Review of the Prior Art
In the diaphragm clutch comprising a diaphragm spring having a continuous peripheral portion which functions as a dished clamping washer and a central portion which has a plurality of radial slits defining a series of fingers and is adapted to co-operate with a clutch release bearing, the diaphragm spring acts as a spring member to cause a pressure plate to clamp the friction facings of a clutch disc between the pressure plate and the flywheel for the transmission of torque during the engagement of the clutch and also serves as a release member to move the pressure plate by being acted on at its finger portion by the clutch release bearing when the bearing is shifted for the disengagement of the clutch. The diaphragm spring provides planar but somewhat conical side faces, alternately concave frontwardly toward the pressure plate or rearwardly toward a clutch cover.
In order to provide fulcrums for the diaphragm spring during both clamping and releasing movements for engagement and disengagement of the clutch, respectively, a pair of wire rings straddle the diaphragm spring intermediate the central portion and the peripheral portion and in contact with its opposite side faces, as shown in U.S. Pat. No. 3,712,436 of Rist. These rings are supported by a number of fastening members, in the form of pillars having flattened heads, which are circumannularly spaced about the drive shaft and extend through a rigidly mounted clutch cover.
However, the wire rings tend to expand radially when subjected to centrifugal action during rotation of the clutch so that the fulcrums are unevenly displaced in a radial direction, depending upon tightness of contact between the flattened pillar heads and the face of the diaphragm spring or between the other face of the diaphragm spring and the clutch cover. Generally, one ring is tightly clamped along at least a portion of its circumference so that radial expansion of the pair of rings is uneven, thereby creating a small but significant moment arm when fulcruming occurs.
Because of the fulcruming action during clutching, moreover, the portions of wire ring between these flattened heads is further subjected to bending axially, roughly in parallel to the drive shaft. In addition, the ring in contact with the pillars is free to rotate while the clutch is disengaged so that both the pillars and the ring tend to become worn. Consequently, it is difficult to retain the pair of wire rings in the predetermined accurate position over a long period of time and the displacement and deformation of the wire rings result in deterioration of the performance of the clutch.
Some of this difficulty is avoided by the construction disclosed in U.S. Pat. No. 3,499,512 of Maurice because the rearward ring is replaced by an annular bead formed in the clutch cover so that a uniform fulcrum is provided on the rearward side face of the diaphragm spring. On the other side face, however, both radial expansion and axial bending can occur between the pillars in spite of the arcuately shaped bead thereon. In order to obviate clutch deterioration, both radial and axial deformation of the fulcrum-providing ring means must be prevented.